It is well known that the epoxidation of olefinic compounds with hydrogen peroxide may be effectively catalyzed by certain synthetic zeolites containing titanium atoms (see, for example, U.S. Pat. No. 4,833,260). While selectivity to the desired epoxide is generally high, U.S. Pat. No. 4,824,976 proposes that the non-selective ring-opening reactions which take place when epoxidation is performed in a protic medium such as water or alcohol may be suppressed by treating the catalyst prior to the reaction or during the reaction with a suitable acid neutralizing agent. The neutralizing agent is said to neutralize acid groups on the catalyst surface which tend to promote by-product formation. Neutralization, according to the patent, may be accomplished with water soluble basic substances chosen from among strong bases such as NaOH and KOH and weak bases such as NH.sub.4 OH, Na.sub.2 CO.sub.3, NaHCO.sub.3, Na.sub.2 HPO.sub.4 and analogous potassium and lithium salts including K.sub.2 CO.sub.3, Li.sub.2 CO.sub.3, KHCO.sub.3, LiHCO.sub.3, and K.sub.2 HPO.sub.4, alkali and/or alkaline earth salts of carboxylic acids having from 1 to 10 carbon atoms and alkali and/or alkaline earth alcoholates having from 1 to 10 carbon atoms.
More recently, as described in U.S. Pat. Nos. 5,646,314, and 5,675,026 it has been found that the presence of certain nonbasic (i.e., neutral or acidic) salts such as lithium chloride, sodium sulfate, lithium nitrate, magnesium acetate and ammonium acetate also improves the selectivity of an epoxidation catalyzed by a titanium-containing zeolite.
In the aforementioned patents, however, all of the substances said to be effective in enhancing the yield of epoxide are ionic in character. That is, the selectivity-improving additives must be capable of dissociation into cationic and anionic species when dissolved in water. There is no teaching or suggestion that any non-ionic compounds might be capable of providing similar benefits when present in an olefin epoxidation system catalyzed by a titanium-containing zeolite.